1. Field of the Invention
This invention relates to loud speakers, and more particularly, to those loud speakers in which vibration damping of the vibrating plate is employed.
2. Description of the Prior Art
In loud speakers, especially in dynamic speakers used in head phones, the resonance frequency of the vibrating plate is high, so that insufficient damping is liable to occur when electromagnetic damping means are employed. For this reason, a damping material such as felt is often mounted on the rear portion of the vibrating plate to obtain uniform reproduction characteristics.
However, since the felt is produced by gathering vegetable fibers, animal hairs, synthetic resin fibers or the like and by compacting these materials closely and entwining them irregularly, the density of the material varies by application of pressure, and the density also depends greatly upon external parameters such as temperature, humidity, etc.
Thus, by the employment of felt as a damping material, stable damping is impossible because of the variation of permeability and by the effect of various parameters acting on the material making up the felt.
Accordingly, it is necessary therefore to obtain uniform sound reproduction characteristics by way of the means or arrangement for mounting the damping material rather than from the material itself. Since the permeability of the material is non-uniform, the damping member must be relatively large in size.